The overall goal of these studies is an understanding of the biochemical processes involved in cell surface changes during fertilization and early development in sea urchin eggs. Four projects that relate to this goal are underway: (1) Factors Involved in Induction of the Acrosomal Reaction in Sperm - Studies have revealed that the Ca 2 ion ionophore is effective in triggering the reaction in which the membrane of the acrosome fuses with the plasma membrane of the sperm. Currently we are investigating the structure of the jelly coat in relation to its role in induction of the acrosomal reaction. (2) The Mechanism of Specific Sperm Egg Interaction - Currently we are accumulating evidence that indicates that a specific glycoprotein on the surface of the egg serves as a species specific receptor for sperm. Current work is concerned with isolation and characterization of the receptor. (3) Isolation and Characterization of the Cortical Granules of the Egg - Techniques have been devised for the isolation of intact cortical granules from homogenates of eggs. The chemical components of the purified cortical granules are being analyzed. Conditions that lead to lysis or fusion of the granules are under investigation. (4) Glycosyl Transferases in Developing Embryos - To determine whether surface glycoproteins play an important role in differentiation and development of sea urchin embryos, the relationship between glycosyl transferase activity and development is being investigated. In particular, two glycosyl transferases are being studied. One catalyzes transfer of galactose to glycoprotein. The other transfers mannose to the sugar carrier lipid, dolichol phosphate. The distribution of these enzymes in specific cell types of the embryo will be investigated.